Lining ducts

ABSTRACT

Apparatus for converting a flexible liner  2  including a layer  3  of composite material comprising thermoplastics material and reinforcing fibres, into a structural member within a duct  1,  has a front portion  6  for insertion in the liner  2,  a central portion  7  for heating one side of the layer  3  and a rear portion  20  which forces the heated layer  3  against the duct  1  for consolidation and cooling under pressure. The central portion  7  has heating means  8  producing hot gas which is forced under pressure through the layer  3  of composite material to heat the layer  3,  and provides an air gap  14  on the opposite side of the layer  3  while heating takes place. This ensures uniform heating of the layer  3,  to melt the thermoplastics material which then mixes intimately with the reinforcing fibres, and is consolidated and cooled to form the structural member.

This invention relates to apparatus and a method for lining ducts withfibre-reinforced thermoplastics composite materials.

The term ‘duct’ as used herein includes pipes, tubes and conduits,whether for conveying fluids (for example, water mains pipes or sewers)or for other purposes.

The ducts used for gas and water supplies are often of cast iron, andfailure due to corrosion is becoming an increasing problem as existingsystems age. It is, for example, estimated that over half of all watermains in the UK have been in service for more than 40 years, and that20% have been in service for more than 80 years. Sewer ducts, which aregenerally of brickwork or concrete, can also fail due to structuraldeterioration of the materials. It is generally cheaper and causes lessdisruption if such ducts are rehabilitated by lining rather than removedand replaced. Various different techniques for lining existing ducts areknown, but there is a demand for more efficient rehabilitationtechniques.

Thus, WO 98/26919 shows a method of lining a duct, using a flexibleliner which includes a layer of composite material made ofthermoplastics and reinforcing fibres. The liner is introduced into theduct, heated to cause the thermoplastics fibres to melt, and thenpressure is applied to mix the molten plastic and reinforcing fibresintimately, and to press the liner into contact with the duct, where itcools and consolidates into a structural member. The heating andapplication of pressure is performed by a robotic device commonly knownas a pig. The pig passes along the inside of the liner, opening it up.The pig has means for heating the liner, and consolidation means whichpress the heated liner against the duct, where it cools andconsolidates. One problem in designing the pig is to ensure that itprovides sufficiently uniform heating of the liner to ensure uniformityof the final structural liner member.

DE-A-39 04 524 shows a method of lining a duct using a liner made onlyof thermoplastics, in this case a non-cross-linked plastics. The lineris introduced into the duct and expanded radially until it comes intocontact with the duct, whereupon it becomes rigid and self-supporting.Expansion is preferably performed mechanically, by a pig which rolls inthe duct. The liner may be heated to assist expansion, for example bywarm air, while there is an air gap between the liner and the duct.However, it is important that the softening temperature of the plasticsis not reached. The liner is therefore heated essentially by conduction,as its construction from thermoplastics means that it is relatively easyto control its temperature.

We have found that heating by conduction is not suitable for a linerdescribed in WO 98/26919, which includes a layer of composite materialcomprising thermoplastics and reinforcing fibres. The composite materialhas air pockets throughout its thickness, and so cannot be heateduniformly to the melting point of the thermoplastics by conduction.

According to a first aspect of the invention, apparatus for converting aflexible liner, including a layer of composite material comprisingthermoplastics material and reinforcing fibres, into a structural memberwithin a duct, comprises a front portion adapted to be inserted in theliner, a central portion having heating means on one side of the layerof composite material, and a rear portion having consolidation means forforcing the heated layer of composite material towards the duct forconsolidation and cooling under pressure to form the structural member,characterised in that the heating means produces hot gas which is forcedunder pressure through the layer of composite material to heat thelayer, and the central portion is constructed and arranged to provide anair gap on the opposite side of the layer of composite material whileheating takes place.

Providing the air gap on the side (inside or outside) of the layer ofcomposite material opposite the heating means assists in the uniformheating of the layer, as it will not be in contact with the duct or partof the apparatus which can adversely affect heating. The air gap is onthe low pressure side of the layer to provide a well-defined exit pathfor the pressurised hot gas through the thickness of the compositelayer. The pressure differential across the layer drives the hot gasthrough in a uniform manner. The hot gas replaces the air in the pocketsin the layer of composite material, and it has been found that this is amajor contributory factor in uniform heating of the layer, and thereforeof the liner as a whole.

The hot gas may be directed from the air gap forwardly to providepreheating of the liner at the front portion.

The hot gas is preferably produced by heating a supply of compressedair. Unheated compressed air may then conveniently be used as theconsolidation means forcing the heated layer of composite material intocontact with the duct. The compressed air inflates a flexible bag meanswhich acts on the layer of composite material. The flexible bag meansmay be attached to the central portion. Alternatively, it may beseparate, and be expanded from the rear, unrolling as it does so. Thishas the advantage of reducing friction between the layer and the bagmeans.

Preferably the central portion has inner and outer members, one of theinner and outer members having the heating means and the other havingsupport means for providing the air gap.

Conveniently, the inner member has the heating means, so that the layerof composite material is heated from the inside, while the outer memberprovides the air gap between the outside of the composite material layerand the duct.

In one embodiment the outer member is annular, surrounding and spacedfrom the inner member, and the layer of composite material is supportedbetween the inner and outer members. In another embodiment the outermember increases in diameter from the front portion to the rear portion,and the layer of composite material is guided on the outside of theouter member. The outer member is preferably frusto-conical. This hasthe advantage of opening up the liner gradually as it is heated.

In yet another embodiment the outer member comprises a support carriagesurrounding and spaced from the inner member. The layer of compositematerial is again supported between the inner and outer members. Thecarriage conveniently has external wheels by which it rolls along insidethe duct.

Alternatively, the outer member has the heating means, so that the layerof composite material is heated from the outside, and the inner memberhas the support means providing the air gap between the inside of thelayer and the inner member. In this embodiment the outer member maycomprise a carriage. The carriage may extend forwardly to surround allor part of the front portion as well.

The liner may include an outer thermoplastics layer between the duct andthe layer of composite material.

The apparatus is conveniently moved along the duct by being winched fromits front portion. Compressed air and power for the heating means aresupplied through lines attached to the apparatus. A mobile unit mayconveniently generate the compressed air supply and the power, forexample electricity, to operate the apparatus.

According to a second aspect of the invention, a method of lining a ductcomprises:

-   inserting into the duct a flexible liner including a layer of    composite material comprising thermoplastics material and    reinforcing fibres;-   producing hot gas on one side of the layer of composite material and    forcing the hot gas under pressure through the layer of composite    material while maintaining an air gap on the opposite side of the    layer, to melt the thermoplastics material;-   applying pressure to the heated layer to force it towards the duct    for consolidation; and-   allowing the liner to cool under pressure whilst in contact with the    duct to harden the layer of composite material into a structural    member.

Thus, maintaining the air gap on the side (inside or outside) of thelayer opposite to that which is being heated assists in the uniformheating of the layer. The hot gas passes through the composite to theair gap, on the low pressure side of the composite layer, and replacesthe air in the pockets of the layer, to heat it uniformly.

The hot gas may then be directed from the air gap to provide pre-heatingof the liner.

The liner is preferably inserted into the duct in a collapsedconfiguration and is subsequently expanded.

Subsequent to insertion of the liner into the duct, apparatus accordingto the first aspect of the invention may be passed through the liner toperform the method.

A third aspect relates to a combination of the apparatus and the linerto provide an efficient rehabilitation technique for lining existingducts.

According to a third aspect of the invention, in a combination ofapparatus and a flexible liner for forming a structural member to line aduct, the liner includes a layer of composite material comprisingthermoplastics material and reinforcing fibres, and is adapted forinsertion into the duct, and the apparatus has a front portion adaptedto be inserted in the liner, a central portion having heating means onone side of the layer of composite material, and a rear portion havingconsolidation means for forcing the heated layer of composite materialtowards the duct for consolidation and cooling under pressure to formthe structural member, characterised in that the heating means produceshot gas which is forced under pressure through the layer of compositematerial to heat the layer, the combination being so constructed andarranged that there is an air gap on the opposite side of the layer ofcomposite material while heating takes place.

The apparatus may be in accordance with the first aspect of theinvention. The liner preferably comprises the layer of compositematerial together with an outer layer of thermoplastics material. Anyother suitable combination of apparatus and liner could also be used.

As with the first two aspects of invention, it is the provision ofpressurised hot gas and the air gap that assists in the uniform heatingof the layer of composite material, to improve the effectiveness of theprocess.

The various aspects of the invention are illustrated, by way of example,in the accompanying drawings, in which:

FIG. 1 shows in diagrammatic form the use of apparatus for lining a ductwith a liner having a layer of composite material;

FIG. 2 shows a longitudinal section through the apparatus of FIG. 1which has internal heating means for the liner;

FIG. 3 shows a longitudinal section through a modified apparatus withexternal heating means for the liner;

FIG. 4 shows a longitudinal section through a modified apparatus withinternal heating means for the liner;

FIG. 5 is similar to FIG. 4, but shows a further modification; and

FIG. 6 is similar to FIG. 5, and shows modified consolidation means.

FIG. 1 illustrates apparatus used for lining an underground duct, inthis case a water mains pipe 1, with a liner 2 of fibre-reinforcedcomposite material to form a structural member.

The liner 2 is initially flexible and includes an inner layer 3 ofcomposite material comprising filaments of thermoplastic and filamentsof reinforcing fibres, and an outer layer 4 of thermoplastics material.Each layer is formed as a tube. The preferred material for the innerlayer 3 is one knitted, braided, woven (or otherwise matted together)from tows comprising substantially continuous filaments of athermoplastic such as polypropylene and similarly continuous reinforcingfibres such as that available from Vetrotex International under theregistered trade name TWINTEX. It is also possible to use shorterlengths of fibres connected together in any suitable way. For example,the short fibres may be matted together with a thermoplastic binder,stitched, needle punched or stapled. The inner layer 3 has air pocketsbetween the filaments.

The apparatus comprises a robotic device 5 (commonly known as a pig)which is moved through a section of liner 2 previously inserted into thepipe 1. The device 5 has a front portion 6, a central portion 7including heating means 8 and support means 9, and a rear portion 10including consolidation means 11. The device 5 is pulled through thepipe 1 by a winch 12 operating a cable 13 attached to the front portion6. The heating means 8 comprises an electrical element (or any othersuitable heater) which heats compressed air, producing hot gas which isthen applied to the inside of the layer 3 to melt the thermoplasticfilaments. The support means 9 provide an air gap 14 on the outside ofthe inner layer 3 between the inner layer 3 and the outer layer 4. Theelectricity for the heating element 8 and the compressed air aresupplied by a generator and compressor respectively formed into a mobileunit 15 which remains above ground, and is connected to the device by anumbilical 25 containing the electricity and air lines. The compressedair is also used for the consolidation means, which comprises a flexiblebag 11 inflated by the compressed air, to press the heated inner layer 3and the outer layer 4 against the internal wall of the pipe 1. Oncooling, the liner 2 forms a structural member within the pipe 1. Themobile unit 15 also includes a programmable process control unit tocontrol operation of the various parts. The apparatus shown willnormally reline about 100 m of pipe in a single run.

FIG. 2 shows the device 5 and the liner 2 in more detail. When the liner2 is inserted in the pipe 1, it tends to fold up at the lowest point ofthe pipe. As the device 5 travels along, the outer layer 4 is firstpressed against the pipe, followed by the inner layer 3.

The front portion 6 of the device 5 comprises a rounded nose 16 havingan eye 17 to which the winch cable 13 is attached. Movement of the nose16 opens up the inner layer 3. The heating element 8 is attached to therear of the nose 16, and is of smaller diameter, so that a gap opens upbetween the heating element 8 and the inside of the inner layer 3. Thehot gas (up to 180° C.) produced by the heating element 8 is underpressure, and is forced through the inner layer 3, by the pressuredifferential across the inner layer 3, between the higher pressureinside surface and the lower pressure air gap 14 on the outside surface.The hot gas drives out the air in the air pockets, thus heating thelayer 3 from the inside. The hot gas reaches the lower pressure air gap14 on the outside of the inner layer 3. The air gap 14 is provided bythe support means 9, which also serves to direct the gas forwardly overthe nose 16. The gas, which is still warm, serves to pre-heat the innerand outer layers 3, 4.

The support means 9 comprises a tubular metal carriage 18 surroundingpart of the nose 16 and the heating element 8, and arranged between theinner and outer layers. Wheels 19 are mounted around the circumferenceof the radially outer side of the carriage 18 to roll along inengagement with the pipe and the outer layer 4. The radially innersurface 20 of the carriage 18 is contoured. A forward rounded annularprojection 21 fits into a corresponding contour of the nose 16, so thatmovement of the nose 16 also pulls the carriage 18 along. Furtherprojections 22, 23, 24 are spaced along the heating element 8 to keepthe inner layer 3 in the correct place.

At the rear portion 10 the inflatable bag 11, which is for example ofsilicone rubber, is attached to the rear of the heating element 8. Whenfilled with compressed air at a suitable pressure, the bag 11 forces thehot inner layer 3 against the outer layer 4 and the pipe 1, toconsolidate and cool it under pressure to form a structural member.

Thus, in use, the liner 2 is first inserted into the pipe 1, perhaps bywinching. The device 5 is then inserted into the liner 2, ensuring thatthe inner layer 3 is between the nose 16 and the carriage 18, and thatthe outer layer 4 is radially outside the carriage 18. The device 5 isthen operated by the control unit to supply compressed air to theheating element 8, to provide hot gas under pressure to heat the innerlayer 3, and then to inflate the bag 11, and operate the winch 12 topull the device 5 along the pipe 1. The control unit controls the gastemperatures and air pressures, and the velocity of the device.

With the device 5 in an initial position the hot gas directed over thenose 16 preheats an initial portion of the liner 2 and urges the outerlayer 4 against the pipe 1. The hot gas also heats the thermoplasticsfilaments of the inner layer 3 uniformly, because the pressuredifferential as a result of the air gap 14 drives the hot gas throughthe thickness of the layer 3, replacing the air in the air pockets withhot gas. The thermoplastics filaments therefore melt and the moltenplastics surrounds the reinforcing fibres. The device moves along apredetermined length, whereupon the bag 11 is inflated to press the hotinner layer 3 and the warm outer layer 4 against the pipe 1. The moltenplastics of the inner layer 3 mixes intimately with the reinforcingfibres, as part of the consolidation of the layers, which then cool andharden under pressure to form a structural member. While the bag 11 isconsolidating the initial portion of the liner, the hot gas is heatingthe next portion, and so the process continues.

The device provides an efficient way of lining the pipe. FIG. 3 shows amodified device, and corresponding reference numerals have been appliedto corresponding parts. Thus, the device 5 of FIG. 3 has the same basicelements as that of FIG. 2, but the heating element 8 is provided on thecarriage 18, rather than being attached between the nose 16 and the bag11. The inner layer 3 is therefore heated from the outside instead ofthe inside. The support means 9 is then formed by a member 26 attachedbetween the nose 16 and the bag 11. The member 26 comprises longitudinalfins 27, so that the required air gap 14 is provided on the inside ofthe inner layer 3. The hot gas is directed forwardly through the nose 16to pre-heat the inner layer 3. Otherwise the embodiment of FIG. 3operates in the same way as that of FIG. 2.

FIG. 4 shows a diagram of a modification of the embodiment of FIG. 2,and corresponding reference numerals have been applied to correspondingparts. In FIG. 4 the heating element 8 is again provided for the insideof the liner 2, and is attached between the nose 16, which is spherical,and the bag 11 (shown uninflated). The support means 9, instead of beinga carriage 18, comprises an annular member 30 surrounding the nose 16and heating element 8, to guide the inner layer 3 and maintain the airgap 14 during heating. The annular member 30 has an enlarged forward end31 round the spherical nose 16, and a tubular rearward end 32 round theheating element 8. The member 30 may have wheels or rollers (not shown)to reduce friction. Otherwise the construction and operation of theembodiment of FIG. 4 are the same as those of FIG. 2.

FIG. 5 shows a modification of the embodiment of FIG. 4. In FIG. 5 thefront portion 6 of the device comprises a toroidal end cap 33 with theeye 17 to which the winch cable 13 is attached. The heating element 8extends between the end cap 33 and the bag 11. The support means 9comprises a perforated frusto-conical member 34 also attached betweenthe cap 33 and the bag 11. The diameter of the member 34 increases fromfront to rear, and the inner layer 3 is guided along the outer surfaceof it. It has been found that the member 34 forms a guide for the innerlayer 3, ensuring that the air gap 14 is maintained between the innerlayer 3 and the pipe 1 during heating. It also opens the inner layer 3up gradually as it is heated, so that consolidation is more efficient.Otherwise the construction and operation of the embodiment of FIG. 5 arethe same as those of FIG. 4.

FIG. 6 shows a modification of the embodiment of FIG. 5. In FIG. 6 thefront portion 6, and central portion with the heating element 8 andconical member 34 are similar to those of FIG. 5, although the conicalmember 34 has a rear end cap 35. The rear portion 10, including theconsolidation means 11 is modified, as it is not attached to the centralportion 7. The consolidation means still has a flexible inflatable bag36, but this is inflated from its rearward end, and caused to unrollagainst the liner 2 as the device 5 moves along. The rolling contactbetween the liner 2 and the bag 36 creates less friction than thesliding contact of FIGS. 2 to 5. It may therefore be possible for thedevice 5 of FIG. 6 to move continuously rather than in indexed steps asin FIGS. 2 to 5.

1. Liner conversion apparatus adapted to convert a flexible liner,including a layer of composite material, said composite materialcomprising thermoplastics material and reinforcing fibres, into astructural member within a duct, comprises a front portion, a centralportion and a rear portion, said front portion being adapted to beinserted in said liner, said central portion having heating means on oneside of said layer of composite material and said rear portion havingconsolidation means for forcing said heated layer of composite materialtowards said duct for consolidation and cooling under pressure to formsaid structural member, wherein said heating means produces pressurisedhot gas, said central portion being so constructed and arranged to forcesaid hot gas under pressure through said layer of composite material toheat said layer, and to provide an air gap on the opposite side of saidlayer of composite material while heating takes place, said centralportion having inner and outer members, one of said inner and outermembers having said heating means and the other having support means forproviding said air gap, said outer member increasing in diameter fromsaid front portion to said rear portion, and, in use, said layer ofcomposite material being guided on the outside of said outer member. 2.Apparatus according to claim 1, wherein said outer member isfrusto-conical.
 3. Apparatus according to claim 1, wherein said linerincludes outer thermoplastics layer between said duct and said layer ofcomposite material.
 4. Apparatus according to claim 1, wherein said hotgas is directed from said air gap forwardly to provide pre-heating ofsaid liner at said front portion.
 5. Apparatus according to claim 1,wherein said hot gas is produced by heating a supply of compressed air.6. Apparatus according claim 1, wherein compressed air is used as saidconsolidation means.
 7. Apparatus according to claim 1, wherein saidconsolidation means comprises a flexible bag means inflatable bycompressed air.
 8. Apparatus according to claim 7, wherein said flexiblebag means is separate from the central portion and, in use, is expandedfrom said rear, unrolling as it does so.
 9. Liner conversion apparatusadapted to convert a flexible liner, including a layer of compositematerial, said composite material comprising thermoplastics material andreinforcing fibres, into a structural member within a duct, comprises afront portion, a central portion and a rear portion, said front portionbeing adapted to be inserted in said liner, said central portion havingheating means on one side of said layer of composite material and saidrear portion having consolidation means for forcing said heated layer ofcomposite material towards said duct for consolidation and cooling underpressure to form said structural member, wherein said heating meansproduces pressurised hot gas, said central portion being so constructedand arranged to force said hot gas under pressure through said layer ofcomposite material to heat said layer, and to provide an air gap on theopposite side of said layer of composite material while heating takesplace, said central portion having inner and outer members, one of saidinner and outer members having said heating means and the other havingsupport means for providing said air gap, said outer member comprising asupport carriage surrounding and spaced from said inner member. 10.Apparatus according to claim 9, wherein said carriage has externalwheels by which it rolls along inside said duct.
 11. Apparatus accordingto claim 9, wherein said carriage extends forwardly to surround all orpart of said front portion.
 12. A method of lining a duct comprising:inserting into the duct a flexible liner including a layer of compositematerial comprising thermoplastics material and reinforcing fibres whichmaterial, at least when heated, is air permeable; producing hot gas onone side of said layer of composite material and forcing said hot gasunder pressure through said layer of composite material from said oneside thereof to the other side thereof while physically supporting saidcomposite material in spaced relation to said duct to maintain an airgap on the said other side of said layer to receive said hot gas passingthrough said composite material, to melt said thermoplastics material;applying pressure to said heated layer to force it towards said duct forconsolidation; and allowing said liner to cool under pressure whilst incontact with said duct to harden said layer of composite material into astructural member.
 13. A method according to claim 12, wherein said hotgas is directed from said air gap to provide pre-heating of said liner.14. A method according to claim 12, wherein said liner is inserted intosaid duct in a collapsed configuration and is subsequently expanded. 15.A method according to claim 12, wherein after insertion of said linerinto said duct apparatus as defined in claim 1 is passed through saidduct to perform said method.
 16. A combination of apparatus and aflexible liner for forming a structural member to line a duct, in whichsaid liner includes a layer of composite material comprisingthermoplastics material and reinforcing fibres which material, at leastwhen heated, is air permeable, and is adapted for insertion into saidduct, and the apparatus has a front portion, a central portion and arear portion, said front portion adapted to be inserted in said liner, acentral portion having heating means on one side of said layer ofcomposite material, and said rear portion having consolidation means forforcing said heated layer of composite material towards said duct forconsolidation and cooling under pressure to form said structural member,wherein said heating means produces hot gas which is forced underpressure through said layer of composite material from said one sidethereof to the other side thereof to heat said layer, the centralportion having inner and outer members, one of said inner and outermembers having said heating means and the other having support means forproviding an air gap on the said other side of said layer of compositematerial to receive said hot gas passing through said composite materialwhile heating takes place.
 17. A combination according to claim 16wherein said liner comprises said layer of composite material togetherwith an outer layer of the thermoplastics material.